1. Field of the Invention
The present invention relates to a conductive rubber member particularly suitable for a conductive roller (e.g., a charge-imparting roller, an image-transfer roller, a development roller, a toner-supply roller, or a cleaning roller), a cleaning blade, a transfer belt, etc., for use in an image-forming apparatus such as an electrophotographic or toner-jet-type copying machine or printer.
2. Background Art
Conductive rubber rollers, which have rubber elasticity and controlled conductivity, are important members in an electrophotographic process. However, the molecule of the rubber for constituting a rubber roller generally does not have resistivity required for the process (104 to 109 Ωcm), and such rubber roller employed in practice is formed from a limited rubber species such as epichlorohydrin rubber. In many cases, in order to ensure required levels of elastic modulus, mechanical strength, and temperature/moisture characteristics, electrical conductivity is imparted to a chemically stable rubber substrate such as silicone rubber, ethylene-propylene rubber (EPDM), or polyurethane through addition thereto of conductive microparticles such as carbon black, and a coating layer on the roller is formed in order to prevent staining of an organic photoconductor (OPC) and other members, adjust resistance of the roller, and prevent electrical, leakage.
In recent years, the melting point of a toner binder for use in an electrophotographic copying machine has become lower and lower. In response to this trend, a development roller is required to have low hardness so as to provide a sufficient deformation to ensure charging of the toner. Japanese Patent application Laid-Open (kokai) No. 2005-283913 discloses a development roller for satisfying the above requirement. The proposed roller, which includes an elastic layer, a urethane resin coating layer, and a thin layer formed of a hardened isocyanate, maintains softness over the entirety of the roller and has a hard surface.
Formation of a coating layer is not preferred, in that cumbersome steps are required, thereby increasing production cost. In an attempt to readily solve the problem, Japanese Patent application Laid-Open (kokai) No. 5-158341 discloses an approach including chemically treating a roller surface. Although the chemical treatment is an effective approach, a surface-treated conductive roller tends to have a hard surface. In practical use of a hardness-reduced roller, the surface of the roller is considerably deformed. Therefore, such a roller is required to have resilience in response to deformation. A roller having a hard surface-treated layer has insufficient resilience in response to deformation and may cause damage to an OPC or other members, and electrical resistance varies during use thereof, which are problematic.
Japanese Patent application Laid-Open (kokai) No. 2007-199694 discloses a conductive roller having a surface-treated layer and maintaining low hardness to a certain extent. However, the surface-treated layer is formed by use of, for example, a surface-treatment liquid which encounters difficulty in entering a conductive elastic layer, and the thus-formed layer is relatively thin. Therefore, the surface-treated layer exhibits insufficient performance in some uses, making the conductive roller unsatisfactory.